Optical transmission link with low bending loss

ABSTRACT

An optical signal transmission link includes a first single mode optical fiber for receiving an optical signal, and a graded index multimode optical fiber for receiving the optical signal from the first single mode optical fiber. The multimode fiber of the transmission link is adapted to support the propagation of greater than or equal to 4 LP modes within the wavelength range of from about 1310 nm to about 1550 nm, has a mode field diameter of the fundamental mode of within the range of from about 3.0 μm to about 14.0 μm within the wavelength range of from about 1300 nm to about 1650 nm, and has a numerical aperture (NA) value of greater than or equal to about 0.16.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical signal transmission link,and more particular to an optical signal transmission link that exhibitsa resistance to bending losses, while maintaining a large mode fielddiameter.

2. Technical Background

The attenuation of a light signal within an optical waveguide fibercaused by bending losses, such as macrobend loss and microbend loss, isan important consideration in the design of optical transmission systemsand components, such as amplifiers, fiber optic devices, fiber opticsensors and integrated optics. While attempts have been made to designthese optical transmission systems and components around bending losses,sharp bending of the associated optical fiber is inherent in someoptical systems, such as amplifiers, miniature delay lines, pay-outsystems, fly-by light systems, Sagnac interferometers, and other similarsystems, components and environments.

Heretofore, the problems associated with bending losses in the abovelisted components and like systems were solved by utilizing highnumerical aperture, reduced core, single mode fibers. However, thesehigh numerical aperture single mode fibers have several drawbacksincluding a limited bending loss performance, significant wavelengthdependency, and relatively small mode field diameters, which areincompatible with standard single mode telecommunication systems.

Therefore, it would be desirable to develop alternative opticaltransmission systems and associated optical transmission links thatprovide a high bending tolerance while maintaining relatively large modefield diameters.

SUMMARY OF THE INVENTION

The present invention meets the need for an optical transmission linkthat provides a high tolerance to both microbending and macrobendingattenuation losses, while maintaining a relatively large mode fielddiameter.

One embodiment of the present invention is to provide an optical signaltransmission link that includes a first single mode optical fiber forreceiving an optical signal, and a graded index multimode optical fiberfor receiving the optical signal from the first signal mode opticalfiber. The multimode optical fiber of the transmission link is adaptedto support the propagation of greater than or equal to four LP modeswithin a wavelength range of from about 1310 nm to about 1550 nm, has amode field diameter of within the range of from about 3.0 μm to about14.0 μm within a wavelength range of from about 1300 nm to about 1650nm, and has a numerical aperture value of greater than or equal to about0.16.

Another embodiment of the present invention relates to an optical signaltransmission link that includes a first single mode optical fiber forreceiving an optical signal, and a graded index multimode optical fiberfor receiving the optical signal from the first single mode opticalfiber. The multimode optical fiber of the transmission link is adaptedto support the propagation of greater than or equal to 4 LP modes withina wavelength range of from about 1310 nm to about 1550 nm. Thetransmission link provides a bending loss of less than or equal to about0.60 dB within a wavelength range of from about 1300 nm to about 1630 nmwhen 1000 loops of the multimode fiber is wrapped about a cylinderhaving a 2.0 mm diameter.

The present invention also includes optical communication systemsemploying optical signal transmission links in accordance with theembodiments described above.

The present invention utilizes a first single mode optical fiber incombination with a graded index multimode optical fiber to provide anoptical signal transmission link that is highly resistant to microbendand macrobend attenuation losses, while simultaneously providing a largemode field diameter.

Additional features and advantages of the present invention will be setforth in the detailed description which follows and will be apparent tothose skilled in the art from the description or recognized bypracticing the invention as described in the description which follows,together with the claims and appended drawings.

It is to be understood that the foregoing description is exemplary ofthe invention only and is intended to provide an overview forunderstanding of the nature and character of the invention as it isdefined by the claims. The accompanying drawings illustrate variousfeatures and embodiments of the invention, which, together with theirdescription serve to explain the principals and operations of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a fiber optic communication systememploying an optical transmission link embodying the present inventionand including a single mode optical waveguide fiber, and a graded indexmultimode optical fiber;

FIG. 2 is a diagram of fiber core diameter versus alpha for a targetedmode field diameter of a fundamental mode signal propagation within themultimode optical fiber;

FIG. 3 is a diagram of Δβ normalized by K₀ versus alpha for a targetedmode field diameter for the multimode optical fiber;

FIG. 4 is a diagram of Δβ normalized by K₀ versus mode field diameterfor various alpha values for the multimode optical fiber;

FIG. 5 is a diagram of macrobend efficiency versus alpha for targetvalues of mode field diameters for the multimode optical fiber;

FIG. 6 is a diagram of macrobend efficiency versus mode field diameterfor target values of alpha for the multimode optical fiber;

FIG. 7 is a diagram of mode field diameter versus alpha for a pluralityof first higher order modes for a first experimental fiber;

FIG. 8 is a diagram of mode field diameter versus alpha for a pluralityof first higher order modes for a second experimental fiber;

FIG. 9 is a diagram of transmission percentage versus force indicatingmicrobend sensitivity for a plurality of multimode optical waveguidefibers each having a 125 μm diameter;

FIG. 10 is a diagram of transmission percentage versus force indicatingmicrobend sensitivity for a plurality of multimode optical waveguidefibers each having a 80 μm diameter; and

FIG. 11 is a schematic view of a fiber optic communication systememploying an alternative embodiment of the transmission link of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

For purposes of the description herein, it is to be understood that theinvention may assume various alternative orientations and stepsequences, except where expressly specified to the contrary. It is alsoto be understood that the specified devices and process illustrated inthe attached drawings and described in the following specification areexemplary embodiments of the inventive concepts defined in the appendedclaims. Hence, specific dimensions and other physical characteristicsrelating to the embodiments disclosed herein are not to be considered aslimiting unless the claims expressly state otherwise.

Definitions

Alpha profile—The refractive index of an alpha profile is defined as:

n=n ₀(1−Δ(r/a)^(α))

where

n is the refractive index at a particular radii,

n₀ is the maximum value of the refractive index of the core (generallyat the core center),

r is the fiber radius,

a is the outer radius of the core,

^(α) is a an exponent referred to as the alpha profile parameter, and

Δ is defined as:

Δ=[(n ₁ ² −n _(c) ²)/2n ₁ ²]

 where

n₁ is the maximum core refractive index (generally at the fiber center),and

n_(c) is the refractive index of the cladding.

Single mode optical fiber—Fiber that supports propagation of only onemode.

Multimode optical fiber—Fiber that supports propagation of more than onemode (typically four to several hundred modes).

Graded index multimode optical fiber—Fiber that supports propagation ofmore than one mode and has a refractive index of the fiber profile thatchanges gradually from fiber core center to fiber core edge. Examplesinclude 1) a parabolic refractive index profile where the index changesproportional to the square of the radius being maximum in the center andminimum at the core edge, 2) a triangular profile where the refractiveindex decreases linerarly proportional to the fiber radius being maximumin the center and minimum at the core edge, and 3) an alpha refractiveindex profile, where a is typically less than 5.

Numerical aperture (NA)—For an optical fiber, the numerical aperture isgiven by:

NA=[(n ₁ ² −n _(c) ²)]^(1/2)

LP Mode—Linearly polarized modes are a solution of the wave equation.

A general representation of the optical signal transmission link 10embodying the present invention is illustrated in FIG. 1. Transmissionlink 10 includes a first single mode optical fiber 12 for receiving anoptical signal represented by and traveling in a direction indicated byan arrow 14, and a graded index multimode optical fiber 16 coupled tosingle mode fiber 12, for receiving optical signal 14 therefrom, andreceiving a bending strain. Transmission link 10 provides high toleranceto bending loss, while simultaneously maintaining a relatively largemode field diameter.

The single mode optical fiber 12 is typically approximately one meter inlength, and provides selective excitation of a fundamental, or nearlyfundamental, mode of propagation of single 14 within a wavelength rangeof from about 1310 nm to about 1550 nm. The multimode optical fiber 16preferably supports the propagation of at least 4 LP modes within awavelength range of from about 1310 nm to about 1550 nm, and morepreferably of greater than 4 LP modes within the same wavelength range.Multimode fiber 16 is provided a mode field diameter of the fundamentalmode of preferably within the range of from about 3.0 μm to about 14.0μm within a wavelength range of from about 1300 nm to about 1650 nm,more preferably of 7.0 μm at a wavelength of about 1310 nm, and mostpreferably of about 9.3 μm at a wavelength of about 1310 nm. Multimodefiber 16 is also provided with a numerical aperture value of preferablygreater than or equal to about 0.16, and more preferably of greater thanor equal to about 0.20. Multimode fiber 16 is further provided with analpha profile having an alpha value of preferably within the range offrom about 0.5 to about 5.0, more preferably of within the range of fromabout 1.0 to about 3.0, and most preferably of within range of fromabout 1.5 to about 2.5. The maximum refractive index difference ofmultimode fiber 16 is preferably greater than or equal to about 0.8%,more preferably greater than or equal to about 1.0%, and most preferablygreater than or equal to 3.0%. In a preferred embodiment, multimodefiber 16 is provided an alpha profile that includes a parabolic index, acore diameter of within the range of from about 10 μm to about 70 μm,more preferably of within the range of from about 15 μm to about 50 μmand most preferably of within the range of from about 20 μm to about 40μm, and a numerical aperture value of greater than or equal to 0.275.

The above optical parameters and physical characteristics oftransmission link 10 provide an optical fiber communication line havinga bending loss of preferably less than or equal to about 0.60 dB withina wavelength range of from about 1300 nm to about 1630 nm when 1000loops of multimode fiber 16 is wrapped about a cylinder having a 2.0 mmdiameter, a more preferred bending loss of less than or equal to 0.50decibels within a wavelength range of from about 1300 nm to about 1630nm when 1000 loops of multimode fiber 16 is wrapped about a cylinderhaving a 5.0 mm diameter, and most preferably of less than or equal 0.50decibels within a wavelength range of about 1300 nm to about 1630 nmwhen 1000 loops of multimode fiber 16 is wrapped about a cylinder havingan 8.0 mm diameter. The derivation and calculations of the abovereferenced optical and physical parameters of single mode fiber 12 andmultimode fiber 16 are described below.

The difference in bending loss between single mode fiber 12 if singlemode fiber 12 comprised the entire transmission link 10, as compared tothe single mode launched multimode optical fiber 16 can be explained byassuming a curved multimode fiber 16 with a curvature radius R, claddinglevel n₁, a maximum core index n₂, and that the local phase velocity ofthe mode in a curved fiber is proportional to the distance r measuredfrom the center of the fiber curvature. The effective refractive indexof the fundamental mode is inversely proportional to r, and isapproximated as, ${{n_{eff}(r)} = {{n_{eff}(R)}\frac{R}{r}}},$

where, n_(eff)(R) is the effective refractive index of the mode at thefiber axis. The phase velocity reaches the limiting velocity of thelight in the medium at a certain distance r_(d) beyond which thefraction of the mode field is no longer guided and radiates away fromthe fiber. The position of the dissociation point r_(d) in the claddingdepends on the absolute value of the effective refractive index in thestraight fiber when approximating the effective refractive index of thefundamental mode at the fiber axis n_(eff)(R) by the effectiverefractive index of the mode in straight fiber. The dissociation pointr_(d) occurs when n₁ equals n_(eff)(r_(d)) and is approximated as,$r_{d} = {R{\frac{n_{eff}(R)}{n_{1}}.}}$

The dissociation point r_(d) shifts deeper into the cladding and thefraction of the field effected by the curvature reduces with an increasein n_(eff)(R), thereby resulting in lower macrobend sensitivity of thefiber. The effective refractive index n_(eff)(R) of the fundamental modewithin multimode fiber 16, which as noted above supports at least fourLP modes, is near the maximum refractive index of the fiber core,thereby resulting in a significantly larger n_(eff)(R)/n₁ ratio as inthe case of a single mode fiber, resulting in a considerably lowermacrobend sensitivity of the fundamental mode in multimode fiber 16.

The bending loss of optical power in a bend of constant curvature Rwithin multimode fiber 16 is approximated as,${\frac{P_{1}}{P_{0}} = {{^{- \alpha_{b}}\left( R_{o} \right)}l}},$

where P₀ is the optical power at the beginning of the curvature, P₁ isthe optical power at the end of the curvature, l is the length of thecurvature, and α_(b) is the bend loss coefficient. As the bending losswithin curved multimode fiber 16 depends on the fraction of the fieldeffected by the curvature, the bending loss within multimode fiber 16 isapproximated by,${{\alpha_{b}\left( R_{0} \right)} = {\frac{\lambda}{\left( {2w} \right)^{2}n} \cdot \frac{P_{radiative}\left( R_{0} \right)}{P_{total}\left( R_{0} \right)}}},$

where λ is the wavelength of signal propagation, P_(radiative) is theportion of the field effected by the curvature, i.e., the field beyondthe dissociation point, P_(total) is the total optical power flowingthrough multimode fiber 16, and w is the mode field diameter ofmultimode fiber 16. It is known that the bending loss coefficient asdefined above can be closely approximated from Maxwell equations if R₀is increased by a factor of 1/0.6. Considering this relationship andphotoelastic effects, wherein the photoelasticity increases theeffective curvature radius by between 20 and 30%, a realistic losscoefficient is approximated by,

 R _(fiber) =c·R ₀,

where R_(fiber) is the real or physical radius of curvature, and c isdefined as 1/0.6·1.2, or 1.39. The loss coefficient is approximated by,${{\alpha_{b}\left( R_{0} \right)} = \frac{\lambda {\int_{x}^{\infty}{\int_{- {{ArcCos}{(\frac{x_{c}}{r})}}}^{{ArcCos}{(\frac{x_{c}}{r})}}{{E^{2}\left( {\rho,\varphi} \right)}\quad {\rho}\quad {\varphi}}}}}{\left( {2w} \right)^{2}n{\int_{0}^{\infty}{\int_{0}^{2\pi}{{E^{2}\left( {\rho,\varphi} \right)}\quad {\rho}\quad {\varphi}}}}}},$

where E is the traversal component of the field in a straight fiber, andρ and φ are cylindrical coordinates, and x_(c) is the dissociation pointmeasured from the fiber center and is defined as,$x_{c} = {\left( {\frac{n_{eff}(R)}{n_{1}} - 1} \right){R.}}$

In the illustrated example, single mode fiber 12 is utilized as thelaunching system for optical signal 14 to ensure excitation of only thefundamental mode within multimode fiber 16. The single mode fiber 12thereby eliminates possible noise that would result from inter-moduleinterference within multimode fiber 16. Multimode fiber 16 includes agraded index core, that confines the fundamental mode to a differentregion of the core from the higher order modes, thereby providing asignificant advantage over step index fibers. Multimode fiber 16 ispreferably provided with a large refractive index gradient, such asthose found in parabolic fibers, wherein the fundamental mode remainsconfined to a narrow region of the core near the fiber axis whilesimultaneously increasing the mode field diameters of the high orderspatial modes. The principal mode groups in graded multimode fiber 16includes sufficiently different mode field diameters that allow forrelatively selective mode launching, and compensate for mismatch andimperfect launching conditions.

The multimode optical fiber 16 is adjusted to match the mode fielddiameter of the multimode fiber 16 with the single mode fiber 12.Specifically, the core diameter of multimode fiber 16 is adjusted whilemaintaining a high n_(eff)/n₂ ratio. The relationship of the mold fielddiameter in an alpha-profile fiber such as multimode fiber 16, isdefined as,${w = {a\left\lbrack {\frac{A}{V^{2/{({a + 2})}}} + \frac{B}{V^{3/2}} + \frac{C}{V^{6}}} \right\rbrack}},$

wherein A=((2/5)[1+4(2/α)^(5/6)])^(1/2),B=exp(0.298/α)−1+1.478(1−exp(−0.077α)), C=3.76 +exp(4.19/α^(0.418)), Vis the normalized frequency of the fiber, and A is the core radius. Asan example, the core diameter of multimode fiber 16 for an alpha valueof 2 is represented by 2a=28.2 μm.

The microbend loss in the single mode launched multimode fiber 16 iscaused primarily by the coupling between the fundamental and firsthigher order mode. The coupled power coefficient between two modes inmultimode fiber 16 submitted to a microbend deformation is defined by,${h = {K\frac{C\left( {\Delta \quad \beta} \right)}{\Delta \quad \beta^{4}}}},$

where Δβ is the difference in the propagation constant of the coupledmodes, and K is proportional to the overlap integral of the modes. TheC(Δβ) is the power spectrum of the curvature, and is defined as,${{C\left( {\Delta \quad \beta} \right)} = {\langle{{\frac{1}{L}{\int_{0}^{L}{\frac{1}{R(z)}^{\quad \Delta \quad {\beta t}}\quad {z}}}}}^{2}\rangle}},$

where R(z) describes the curvature function of a perturbed fiber. As isknown in the art, the curvature power spectrum can be approximated by,${{C\left( {\Delta \quad \beta} \right)} = \frac{C_{0}}{\Delta \quad \beta^{2p}}},$

where C₀ is constant and p=1,2. The microbend loss of the single modelaunched multimode fiber 16 depends primarily on the Δβ between thefundamental and first higher order modes. The coupled power coefficientincreases proportionally to about 1/Δβ⁶, thereby indicating that anincrease in Δβ of about 50% increases the coupling coefficient more thanan order of magnitude. The Δβ between the fundamental and first higherorder modes must be as large as possible in order to assure lowmicrobend sensitivity of the system. This is determined by defining thedifference in the propagation constant of the coupled modes as,${{\Delta \quad \beta} = {\sqrt{\frac{\alpha}{\alpha + 2}}\frac{2\sqrt{\Delta}}{a}\left( \frac{m}{M} \right)^{\lbrack{{({a - 2})}/{({a + 2})}}\rbrack}}},$

where m is the modal group label, e.g., m=1 for Δβ between the first andsecond mode, α is the core radius, and M is the number of modal groupsexpressed as, $M = {\frac{\alpha}{\alpha + 2}a^{2}k^{2}{\Delta.}}$

EXAMPLES

The optical and physical parameters of the following examples werecalculated utilizing design software FIBER CAD 1.0, commerciallyavailable from Optiwave, Inc. of Ottawa, Ontario, Canada.

Modeled Example A includes a multimode fiber compatible with standardsingle mode systems and a common numerical aperture. The multimode fiberof Example A includes an alpha-profile, having a numerical aperturevalue of 0.275 and a targeted fundamental mode field diameter of 2w=9.3μm at a wavelength of 1310 nm. Modeled Example B includes a multimodefiber having a reduced mode field diameter compatible with a highnumerical aperture, bend resistive single mode system. The multimodefiber utilized in Example B includes an alpha-profile, a numericalaperture value of 0.275, and a targeted fundamental mode field diameterof 2w=6.6 μm at a wavelength of 1310 nm. In both examples, the corediameter of the associated multimode fiber is varied until the desiredmode field diameter is obtained. FIG. 2 charts the fiber core diametervs. alpha for the targeted mode field diameter of the multimode fiber.As is illustrated in FIG. 2, the core size increases rapidly for analpha value of less than 1 for the multimode fiber of Example A.

FIG. 3 illustrates the Δβ between the fundamental mode and the nexthigher order mode in β space. It should be noted that Δβ is highlydependent on the mode field diameter of the multimode fiber with verylittle dependence on alpha for alpha values of greater then 0.5. Alongthe same lines, FIG. 4 illustrates Δβ vs. mode field diameter for fiberswith varying alpha values. FIG. 4 indicates that Δβ depends almostcompletely on the mode field diameter and wavelength and is nearlyindependent of the alpha value. The ratio of (n_(eff)−n₁)/(n₂−n₁), asshown in FIG. 4, is the fiber “macrobend efficiency,” i.e., the abilityof the multimode fiber to take advantage of the available indexdifference to achieve a high n_(eff). A fiber with a ratio of 1 has themaximum possible macrobend resistance for any given numerical aperturevalue, while a fiber with a ratio close to 0 is highly sensitive tomacrobends. As shown in FIG. 5, fiber macrobend efficiency drops rapidlyat low values of alpha, however, changes very little for alpha valuesabove 2.

FIG. 6 illustrates the ratio of (n_(eff)−n₁)/(n₂−n₁) vs. the mode fielddiameter for fibers with different values of alpha as compared to thoseillustrated in FIG. 4. The fibers of FIG. 6 were provided a numericalaperture value of 0.275 at a wavelength of 1310 nm. As indicated in FIG.6, small mode field diameters correspond with significant reduction inmicrobend efficiency in the multimode fibers.

FIGS. 7 and 8 illustrate the mode field diameters of the four closestspatial neighbors of the fundamental mode vs. a parameter alpha fordesign examples A and B. The difference in the mode field diameterbetween the fundamental mode and the higher order modes decrease withalpha, thereby indicating that utilizing a multimode fiber with a lowalpha is advantageous to fibers with a high alpha. In order to allowsimple and effective fundamental mode launch it is desirable to choosefibers having low alpha values. However, reduction of the alpha valuealso reduces macrobend resistance, i.e., the ratio (n_(eff)−n₁)/(n₂−n₁),with this effect becoming increasingly important for mode field diameterbelow 6 μm at wavelengths of about 1310 nm, or for fibers wherein alphais less than 1.

The Δβ between the fundamental mode and the first higher order modedepends nearly solely on the mode field diameter for fiber with an alphavalue of greater than 1. The microbend sensitivity of the fiber,therefore, predominantly depends on the mode field diameter of the fiberdue to the highly non-linear relationship between Δβ and the couplingcoefficient. The influence of the fiber profile is reflected onlythrough the overlap integral between the fundamental mode and the higherorder modes. As a result, fibers with the same mode field diameter anddifferent alpha values experience different macrobend sensitivity, andfibers with lower alpha values are less sensitive to microbend loss thanfibers with higher alpha values.

Table 1 lists the physical parameters for a pair of fibers Examples 1and 2, as constructed and tested.

TABLE 1 Physical Parameters of Example Fibers 1 and 2 Example 1 Example2 Core size (μm) 28.6 37.6 NA 0.27 0.27 Outer diameter 80 125 α 2 2 Modefield diameter (μm) at 1310 9.1 10.4

The macrobend test results for Examples 1 and 2 are summarized in Table2, wherein d is the diameter of the cylinder about which the multimodefibers where spooled.

TABLE 2 Bend Loss For Example Fibers 1 and 2 Example 1 Example 2 d(mm)Bend Loss (dB) d(mm) Bend Loss (dB)  10 loops 1.3 <0.02 2.1 <0.02  100loops 1.6 <0.15 2.6 <0.05 1000 loops 1.6 <0.63 3.1 <0.064

A sandpaper test was used to compare microbend performance of the fibersof Examples 1 and 2 by depressing a 1.2 m length of each fiber betweentwo flat steel plates covered by sandpaper (P1000 and P600). Separatetests and comparisons were performed for fibers having outer diametersof 125 μm and 80 μm, the results of which are illustrated in FIGS. 9 and10, respectively.

The optical signal transmission link 10 manufactured in accordance withthe present invention may be used in an optical fiber communicationsystem 18, as illustrated in FIG. 1. System 18 includes an opticaltransmitter 20 adapted to transmit signal 14 through signal mode opticalfiber 12 and multimode optical fiber 16. System 18 also includes anoptical receiver 22 for receiving optical signal 14.

In an alternative embodiment transmission link 10 a (FIG. 11) includes asingle mode optical fiber 12 a and a multimode optical fiber 16 asimilar to single mode optical fiber 12 and multimode optical fiber 16described above. Since transmission link 10 a and optical fibercommunication system 18 a are similar to previously describedtransmission link 10 and optical fiber communication system 18, similarparts appearing in FIG. 1 and FIG. 11 respectively are represented bythe same, corresponding reference numeral, except for the suffix “a” inthe numerals of the latter. The transmission link 10 a further includesa single mode fiber that coupled multimode fiber 16 a to receiver 22 a,thereby ensuring single mode operation of system 18 a. In most systems,both ends of transmission link 10 a will be capable of two-way signaltransmission, and transmitter 20 a and receiver 22 a are shown forillustration only.

The present invention utilizes a first single mode optical fiber incombination with a graded index multimode optical fiber to provide anoptical signal transmission link that is highly resistant to microbendand macrobend attenuation losses, while simultaneously providing a largemode field diameter.

It will become apparent to those skilled in the art that variousmodifications to the preferred embodiment of the invention as describedherein can be made without departing from the spirit or scope of theinvention as defined in the appended claims. Thus, it is intended thatthe present invention covers the modifications and variations of thisinvention provided they come within the scope of the appended claims andthe equivalents thereto.

What is claimed is:
 1. An optical signal transmission link, comprising:a first single mode optical fiber for receiving an optical signal; and agraded index multimode optical fiber for receiving the optical signalfrom the first single mode optical fiber, wherein the multimode fiber isadapted to support the propagation of greater than or equal to 4 LPmodes within a wavelength range of from about 1310 nm to about 1550 nm,the multimode fiber has a mode field diameter of the fundamental mode ofwithin the range of from about 3.0 μm to about 14.0 μm within awavelength range of from about 1300 nm to about 1650 nm, and wherein themultimode fiber has a numerical aperture (NA) value of greater than orequal to about 0.16 and a refractive index profile of the multimodeoptical fiber is substantially unchanged along an entire length thereofand wherein the multimode fiber provides a bending loss of less than orequal to about 0.60 dB within a wavelength rant of from about 1300 nm toabout 1630 nm when 1000 loops of the multimode fiber is wrapped about acylinder having a 2.0 mm diameter.
 2. The transmission link of claim 1,wherein the bending loss of the multimode fiber is less than or equal toabout 0.50 dB within a wavelength range of from about 1300 nm to about1630 nm when 1000 loops of the multimode fiber is wrapped about acylinder having a 5.0 mm diameter.
 3. The transmission link of claim 2,wherein the bending loss of the multimode fiber is less than or equal toabout 0.50 dB within a wavelength range of from about 1300 nm to about1630 nm when 1000 loops of the multimode fiber is wrapped about acylinder having an 8.0 mm diameter.
 4. The transmission link of claim 1,wherein the mode field diameter of the multimode fiber of thefundamental mode is about 7.0 μm at a wavelength of about 1310 nm. 5.The transmission link of claim 1, wherein the mode field diameter of themultimode fiber of the fundamental mode is about 9.3 μm at a wavelengthof about 1310 nm.
 6. The transmission link of claim 1, wherein thenumerical aperture (NA) value of the multimode fiber is greater than orequal to about 0.20.
 7. The transmission link of claim 1, wherein thegraded index of the multimode fiber includes a parabolic index.
 8. Thetransmission link of claim 7, the multimode fiber has a core diameter ofwithin the range of from about 10 μm to about 70 μm.
 9. The transmissionlink of claim 7, wherein the multimode fiber has a core diameter ofwithin the range of from about 15 μm to about 50 μm.
 10. Thetransmission link of claim 8, wherein the multimode fiber has a corediameter of within the range of from about 20 μm to about 40 μm.
 11. Thetransmission link of claim 8, wherein the numerical aperture (NA)valueof the multimode fiber is greater than or equal to about 0.275.
 12. Thetransmission link of claim 1, wherein the multimode fiber has an alphaprofile with an alpha value (α) of within the range of from about 0.5 toabout 5.0.
 13. The transmission link of claim 12, wherein the alphavalue (α) of the multimode fiber is within the range of from about 1.0to about 3.0.
 14. The transmission link of claim 13, wherein the alphavalue (α) of the multimode fiber is within the range of from about 1.5to about 2.5.
 15. The transmission link of claim 1, wherein multimodefiber has a maximum refractive index difference (Δ) of greater than orequal to about 0.8%.
 16. The transmission link of claim 15, wherein themaximum refractive index difference (Δ) of the multimode fiber isgreater than or equal to about 1.0%.
 17. The transmission link of claim16, wherein the maximum refractive index difference (Δ) of the multimodefiber is greater than or equal to about 3.0%.
 18. The transmission linkof claim 1, further including: a second single mode optical fiber forreceiving the optical signal from the multimode optical fiber, whereinthe second single mode fiber is adapted to ensure propagation of only asingle mode to an optical receiver.
 19. An optical fiber communicationsystem, comprising: an optical transmitter adapted to transmit anoptical signal; a first single mode optical fiber for receiving theoptical signal from the transmitter; a graded index multimode opticalfiber for receiving the optical signal from the first single modeoptical fiber, wherein the multimode fiber is adapted to support thepropagation of greater than or equal to 4 LP modes within a wavelengthrange of from about 1310 nm to about 1550 nm, the multimode fiber has amode field diameter of the fundamental mode of within the range of fromabout 3.0 μm about 14.0 μm within a wavelength range of from about 1300nm to about 1650 nm, and wherein the multimode fiber has a numericalaperture (NA) value of greater than or equal to about 0.16 and arefractive index profile of the multimode optical fiber is substantiallyunchanged along an entire length thereof and wherein the multimode fiberprovides a bending loss of less than or equal to about 0.60 dB within awavelength range of from about 1300 nm to about 1630 nm when 1000 loopsof the multimode fiber is wrapped about a cylinder having a 2.0 mmdiameter; and an optical receiver for receiving the optical signal fromthe multimode fiber.
 20. The communication system of claim 19, furtherincluding: a second single mode optical fiber for receiving the opticalsignal from the multimode optical fiber, wherein the second single modefiber is adapted to ensure propagation of only a single mode to theoptical receiver.
 21. An optical signal transmission link, comprising: afirst single mode optical fiber for receiving an optical signal; and agraded index multimode optical fiber for receiving the optical signalfrom the first single mode optical fiber, wherein the multimode fibersupports the propagation of greater than or equal to 4 LP modes within awavelength range of from about 1310 nm to about 1550 nm, and wherein themultimode fiber provides a bending loss of less than or equal to about0.60 dB within a wavelength range of from about 1300 nm to abut 1650 nmwhen 1000 loops of the multimode fiber is wrapped about a cylinderhaving a 2.0 mm diameter and a refractive index profile of the multimodeoptical fiber is substantially unchanged along an entire length thereof.22. The transmission link of claim 21, wherein the bending loss of themultimode fiber is less than or equal to about 0.50 dB within awavelength range of from about 1300 nm to about 1630 nm when 1000 loopsof the multimode fiber is wrapped about a cylinder having a 5.0 mmdiameter.
 23. The transmission link of claim 22, wherein the bendingloss of the multimode fiber is less than or equal to about 0.50 dBwithin a wavelength range of from about 1300 nm to about 1630 nm when1000 loops of the multimode fiber is wrapped about a cylinder having a8.0 mm diameter.
 24. The transmission link of claim 21, wherein themultimode fiber has a mode field diameter of the fundamental mode withinthe range of from about 3.0 μm about 14.0 μm within a wavelength rangeof from about 1300 nm to about 1650 nm.
 25. The transmission link ofclaim 24, wherein the mode field diameter of the multimode fiber of thefundamental mode is about 7.0 μm at a wavelength of about 1310 nm. 26.The transmission link of claim 25, wherein the mode field diameter ofthe multimode fiber of the fundamental mode is about 9.3 μm at awavelength of about 1310 nm.
 27. The transmission link of claim 21,wherein multimode fiber has a numerical aperture (NA) value of greaterthan or equal to about 0.16.
 28. The transmission link of claim 27,wherein the numerical aperture (NA) value of the multimode fiber isgreater than or equal to about 0.20.
 29. The transmission link of claim21, wherein the graded index of the multimode fiber includes a parabolicindex.
 30. The transmission link of claim 29, wherein the multimodefiber has a core diameter of within the range of from about 10 μm toabout 70 μm.
 31. The transmission link of claim 30, wherein themultimode fiber has a core diameter of within the range of from about 15μm to about 50 μm.
 32. The transmission link of claim 31, wherein themultimode fiber has a core diameter of within the range of from about 15μm to about 50 μm.
 33. The transmission link of claim 30, wherein themultimode fiber has a numerical aperture (NA) value of greater than orequal to about 0.275.
 34. The transmission link of claim 21, wherein themultimode fiber has an alpha profile with an alpha value (α) of withinthe range of from about 0.5 to about 5.0.
 35. The transmission link ofclaim 34, wherein the alpha value (α) of the multimode fiber is withinthe range of from about 1.0 to about 3.0.
 36. The transmission link ofclaim 35, wherein the alpha value (α) of the multimode fiber is withinthe range of from about 1.5 to about 2.5.
 37. The transmission link ofclaim 21, wherein multimode fiber has a maximum refractive indexdifference (Δ) of greater than or equal to about 0.8%.
 38. Thetransmission link of claim 37, wherein the maximum refractive indexdifference (Δ) of the multimode fiber is greater than or equal to about1.0%.
 39. The transmission link of claim 38, wherein the maximumrefractive index difference (Δ) of the multimode fiber is greater thanor equal to about 3.0%.
 40. The transmission link of claim 21, furtherincluding: a second single mode optical fiber for receiving the opticalsignal from the multimode optical fiber, wherein the second single modefiber is ensures propagation of only a single mode to an opticalreceiver.
 41. An optical fiber communication system, comprising: anoptical transmitter for transmitting an optical signal; a first singlemode optical fiber for receiving the optical signal from thetransmitter; a graded index multimode optical fiber for receiving theoptical signal from the first single mode optical fiber, wherein themultimode fiber supports the propagation of greater than or equal to 4LP modes within a wavelength range of from about 1310 nm to about 1550nm, and wherein the multimode fiber provides a bending loss of less thanor equal to about 0.60 dB within a wavelength range of from about 1300nm to abut 1650 nm when 1000 loops of the multimode fiber is wrappedabout a cylinder having a 2.0 mm diameter and a refractive index profileof the multimode optical fiber is substantially unchanged along anentire length thereof; and an optical receiver for receiving the opticalsignal from the multimode fiber.
 42. The communication system of claim41, further including: a second single mode optical fiber for receivingthe optical signal from the multimode optical fiber, wherein the secondsingle mode fiber ensures propagation of only a single mode to theoptical receiver.